1. Field of the Invention
The present invention relates to an angular rate sensor for use in various electronic devices, concerning posture control, navigation and the like of a movable object such as an aircraft, an automobile, a robot, a ship, and a vehicle.
2. Description of the Related Art
In the following, a conventional angular rate sensor is described.
FIG. 9 is a plan view of an oscillator of the conventional angular rate sensor. FIG. 10 is a partially see-through perspective view of the angular rate sensor.
The conventional angular rate sensor calculates an angular rate by oscillating e.g. a tuning-fork-shaped oscillator 1, and electrically detecting distortion of the oscillator 1 caused by a Coriolis force. Normally, an angular rate with respect to one axis of rotation can be calculated with use of a single angular rate sensor.
Various shapes are proposed concerning the shape of the oscillator 1 to be used in the angular rate sensor, such as tuning-fork shape, H-shape, and T-shape. For instance, the tuning-fork shaped oscillator 1 includes a U-shaped portion 3 with a pair of arm portions 2, and a bar-like stem portion 4 continuously formed to the U-shaped portion 3.
The oscillator 1 is connected to a computation processing circuit 5 for electrically detecting distortion of the arm portions 2 caused by a Coriolis force and performing a computation process to calculate an angular rate of the object. The computation processing circuit 5 is fabricated on a circuit board 6, and the oscillator 1 is mounted on the circuit board 6. The angular rate sensor is constructed by encasing the oscillator 1 and the circuit board 6 in a case 7. There is known, as prior art document information relating to the invention of the application, Japanese Unexamined Patent Publication No. 2002-243451, for instance.
Generally, in the oscillator 1 of the angular rate sensor, the masses of the arm portions 2 in pair may not be completely identical to each other due to variation in the manufacturing process thereof.
In the above arrangement, if an angular rate is generated in a condition that the arm portions 2 are oscillated in a direction toward or away from each other, for instance, the arm portions 2 are distorted in a direction orthogonal to the oscillating direction caused by a Coriolis force. However, if the arm portions 2 are oscillated in a condition that the masses of the arm portions 2 in pair are not completely identical to each other, or a like condition, the arm portions 2 may be distorted in a direction other than the oscillating direction of the arm portions 2 even if an angular rate is not generated (hereinafter, this distortion is called as “false distortion”). As a result, an unwanted signal may be outputted resulting from the false distortion, which may cause a characteristic degradation concerning the angular rate sensor.